Many systems require a variable speed fan (or blower) to control circuitry temperature and/or heat output. Control of the fan can be accomplished using a series-pass circuit, however this solution generates too much heat and is energy wasteful. Alternatively, fan control can be accomplished using a standard pulse-width-modulated (PWM) power control circuit. Generally, a microcontroller generates a precisely-timed pulse train to drive the power switching circuitry, which outputs a desired voltage that drives the fan. However, the PWM arrangement has several shortcomings. First, there are a number of relatively large discrete components needed to generate, filter and regulate the PWM output voltage. When a power source is significantly above the maximum operating voltage of the fan, extra protection circuitry is needed to prevent a catastrophic failure in the event of a microcontroller crash. An inexpensive microcontroller's software-timing and clock-rate require the PWM circuitry to be designed to operate at a relatively low frequency, thus making the PWM arrangement less efficient and physically larger. Moreover, the microcontroller must communicate in real time with one or more host devices while performing the PWM power supply control as well as other functions; thus, resulting in a difficult and costly firmware programming challenge.
Accordingly, it is an object of the present invention to provide a fan controller system, and a PWM power supply control system, that removes the real-time power control functions from the microcontroller, thereby reducing the parts-count, energy waste and firmware complexity of such systems.